So-called ashing furnaces have been used to determine the weight loss of a specimen as one or more of its constituents are burned off. A typical ashing furnace includes an enclosure, a heating element for applying heat to and combusting the combustible portion of the material within the enclosure, and a weigh scales for weighing the specimen before, during and after one or more of its combustible constituents are burned off.
One application of ashing furnaces is in the area of asphalt ashing where it is desired to determine the binder content in asphalt by burning the binder off from a sample of asphalt. Asphalt typically is comprised of 93 1/2% by weight rock, sand and other particulate matter, for example rock dust, 6% light crude (binder) and 1/2% other matter. The sample of asphalt is weighed before combustion and after combustion. Combustion occurs at approximately 1,000.degree. F., a temperature at which the 931/2% by weight rock, sand and particulate matter is inert. The sample is weighed after its weight rate of change with respect to time is approximately zero (i.e. weight change stabilizes), and the post-combustion weight is compared to the precombustion weight to determine the weight of the binder burned off and thus contained within the starting sample.
One drawback of conventional ashing furnaces is that the furnace does not completely combust the combustible portion of the sample. As such, uncombusted products of combustion escape out of the furnace through an exhaust port. Discharging the uncombusted products of combustion into the atmosphere is of course undesirable from an environmental standpoint.
One solution to provide more complete combustion is with the use of a so-called catalytic converter, wherein exhaust gases produced by combustion of a material are trapped in a catalytic material and the residual heat in the exhaust provides additional secondary combustion of the gaseous material. The drawback with catalytic conversion is the inability to control the secondary combustion temperature. That is to say, the temperature of the primary combustion exhaust gases effectively determines the temperature at which secondary combustion occurs in the catalytic converter, which limits the amount of material that can be combusted secondarily.
Another solution is to provide dual combustion chambers with separate heating elements, such that uncombusted products of combustion in the first combustion chamber may be combusted more completely in the second combustion chamber. The disadvantage of such a device is that it is costly to manufacture due to duplication of the chambers. Further, the gaseous material may pass through the secondary combustion chamber too quickly to allow full secondary combustion.
It is therefore a main objective of the present invention to provide an ashing furnace which reduces the discharge of uncombusted products of combustion into the atmosphere.
It is another objective of the present invention to provide an ashing furnace which provides for more complete combustion of the combustible material.
It is yet another objective of the present invention to provide an ashing furnace which provides secondary combustion, the temperature at which is not dependent upon the exhaust gases of the primary combustion.
It is still another objective of the present invention to provide an ashing furnace which provides secondary combustion but which does not require separate combustion chambers.